Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
In the normal ankle and foot there is an anatomical chain of movement from the ankle joint to the toes. In particular, a normal foot has a series of articulations with increasing levels of motion, including the talocrural (ankle) joint, the subtalar (heel) joint, the tarsal (midfoot) joint, and the metatarsals and phalanges (forefoot). The sequence of the articulations of a normal foot permits variations in lateral motions depending on the surface coming into contact with the foot, or the position of the body above the foot. When lower extremity amputations result due to abnormal development, trauma, diabetes, or some other medical condition, these amputations of the leg or ankle result in chronic disability. This is because conventional prosthetic foot designs do not sufficiently replace the anatomical function of the foot to accommodate sideways motions. As such, mediolateral stresses remain a significant problem with current prosthetics, especially on slide-slopes, uneven ground, turning, or where there is uncertainty of placement of the foot such as during cognitive tasks while ambulating.
Pain and skin breakdown at the residual limb remains a problem in current prosthetics in part because of shear stresses induced by forces on the socket. Skin breakdown may cause limitations in many activities of daily living. Additionally, gait is an attention-demanding task, and any concurrent cognitive task, even a very simple one, may disrupt walking performance. The current mechanical designs of existing prostheses are believed to be related to back pain, residual limb pain, and contralateral knee pain along with early osteoarthritis. As a result, many aspects of an individual's physical performance are chronically affected with use of a prosthetic device, not only those associated with walking. If physical activity is reduced, chronic diseases such as cardiovascular disease or impaired glucose metabolism are at increased risk.